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US 5,844,974 AGranted
Emergency telephone communications system
AssigneeNEC Corporation
InventorYasuyo Ichikawa
Life of this patent
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AssigneeNEC Corporation
InventorYasuyo Ichikawa
Estimating the term…
An emergency telephone communications system allows communications during congestion in the event of disaster. The system includes an exchange and telephones connected to the line circuits thereof. The exchange sends a congestion generation signal to a control section to initiate emergency processing when a congestion detecting circuit detects more than a predetermined number of the line circuits in the off-hook state. The control section has a congestion management table listing subscribers and stores not-yet-serviced subscribers when congestion has occurred. The not-yet-serviced subscribers are successively selected from the congestion management table, and calling signals are sent to their telephones. When the subscribers go off-hook within a predetermined time, the control section controls the emergency dial pulse receiver circuit to be ready for reception, and then controls the switch to connect an emergency service trunk to the line circuits to send a tone signal or a voice message. Upon receipt of telephone numbers of the receiving parties sent from the subscribers, the exchanges at the receiving parties are called through the emergency trunk circuit. The telephones send telephone numbers of the receiving parties at a predetermined time after detection of incoming calls from the exchange, or after detection of a given signal.
An emergency telephone communications system for communicating a telephone signal during congestion of an exchange, comprising:
An exchange for use in an emergency telephone communications system, comprising:
A telephone exchange which has line circuits connected to subscriber lines, trunk lines and switches, and serves to connect the lines, further comprising:
Dependencies are inferred from the claim text.